1. Field of the Invention
The present invention relates to a lens drive system which can be used for digital cameras.
2. Description of the Related Art
As an example of a conventional digital camera, a digital camera wherein a camera body is provided with a movable lens frame which supports a lens group, and is further provided in the camera body with a lens drive motor and a lens drive mechanism so that the movable lens frame is driven by the lens drive motor via the lens drive mechanism to move in an optical axis direction between an accommodation position, wherein the movable lens frame is accommodated within the camera body, and an extended position (ready-to-photograph position), wherein the lens frame projects forward from the front of the camera body, is known in the art.
In this type digital camera, if the camera is accidentally dropped on the ground with the movable lens frame in the extended position, the movable lens frame may hit the ground to thereby cause the rear end of the movable lens frame to impact against an inner part of the camera body behind the rear end of the movable lens frame. If this happens, the lens drive mechanism may be damaged. To prevent this problem from occurring, it is sometimes the lens drive mechanism is provided with a half nut which is normally engaged with a feed screw (feed screw shaft), but is disengaged from the feed screw to slide on the feed screw when more than a predetermined force is applied to the half nut in the axial direction thereof. Such a half nut prevents the lens drive mechanism from being damaged to some extend. However, if the movable lens frame is forced to retreat beyond the range of movement thereof, the lens drive mechanism may be totally damaged. As a consequence, the lens frame may remain jammed even if the lens drive motor is driven again.
To prevent such a problem from occurring, it is known in the art to provide in the camera, behind the movable lens, with some type of stop member which prevents the movable lens frame from retreating beyond the range of movement thereof. However, the placement and the size and shape of such stop member are limited in a digital camera which is designed extremely small and compact.
The present invention provides a lens drive system which is structured so as not to be deformed or damaged even if a large external force is unintentionally applied to the movable lens frame to thereby cause the movable lens frame to retreat beyond the range of movement thereof, while making effective use of an inner space of the camera body.
The present invention further provides a lens drive system which is structured so that the optical axis of the lens group supported by the movable lens frame does not easily tilt upon contact of the movable lens frame with the stop member.
For example, in an embodiment, a lens drive system is provided, including a lens case which supports an image pick-up device; a movable lens frame which supports a lens group via which an image is focused on the image pick-up device, the movable lens frame being guided linearly in an optical axis direction thereof, the front of the movable lens frame being projectable forward from the lens case; a reversible motor which is supported by the lens case; a feed screw supported by the lens case to be driven by the reversible motor; a half nut which moves together with the movable lens frame in the optical axis direction, wherein the half nut is normally engaged with the feed screw, and is disengaged from the feed screw to slide on the feed screw when more than a predetermined force is applied to the half nut in the optical axis direction; and a plurality of ribs formed integral with the lens case which project from an inner surface of the lens case behind a space for movement of the movable lens frame. Each of the plurality of ribs includes a stop surface formed at an end of the each rib which faces the movable lens frame, the stop surfaces coming into contact with a rear surface of the movable lens frame when the movable lens frame retreats while the half nut is sliding on the feed screw.
It is desirable for the number of the plurality of ribs to be more than two.
The plurality of ribs can define a plane which is perpendicular to the optical axis.
The lens drive system can be provided in a digital camera.
The movable lens frame can be guided in the optical axis direction between an extended position, wherein the movable lens frame projects forward from a front wall of the digital camera, and an accommodation position wherein the movable lens frame is fully accommodated in the digital camera.
It is desirable for the movable lens frame to be biased forwardly, toward the extended position, by a spring member.
It is desirable for the movable lens frame to include at least one guide projection which is slidably engaged in a guide groove formed on an inner surface of the lens frame.
In another embodiment, a lens drive system of a camera is provided, including a movable lens frame which supports an image-forming lens group, and is guided linearly in an optical axis direction to be movable between an extended position, wherein the movable lens frame projects forward from a front wall of the camera, and an accommodation position wherein the movable lens frame retracts into the camera; a feed screw which extends in the optical axis direction; a motor which can rotate the feed screw in forward and reverse directions about an axis thereof; a half nut which moves together with the movable lens frame in the optical axis direction, wherein the half nut is normally engaged with the feed screw, and is disengaged from the feed screw to slide on the feed screw when more than a predetermined force is applied to the half nut in the optical axis direction; a support member which supports the movable lens frame, the feed screw, the motor and the half nut; and a plurality of ribs formed integral with the support member which project inwards from an inner surface of the support member behind a space for movement of the movable lens frame. A front end face of each the plurality of ribs comes into contact with a rear surface of the movable lens frame when the movable lens frame retreats beyond the accommodation position thereof while the half nut is sliding on the feed screw.
It is desirable for the front end faces of the plurality of ribs to lie in a plane perpendicular to the optical axis direction.
The present disclosure relates to subject matter contained in Japanese Patent Applications No.2001-164058 (filed on May 31, 2001), which is expressly incorporated herein by reference in its entirety.